🔖 Barcode Encoder/Decoder — Code 11 & Code 93

Final Java programming project for the first year of the Higher Degree in Multiplatform Application Development (DAM).

---

📋 Description

A Java implementation of an encoder and decoder for two barcode standards: Code 11 and Code 93 Extended. The project covers the full cycle: encoding a text string into a visual bar representation, and decoding a bar representation back into the original text, including normalization to handle bars of variable widths.

---

📦 Project Structure

├── Code11.java          # Code 11 implementation
├── Code93.java          # Code 93 Extended implementation
├── Code11Test.java      # Code 11 tests
└── Code93Test.java      # Code 93 Extended tests

---

🔢 Code 11

What is it?

Code 11 is a high-density barcode designed primarily for the telecommunications industry. It encodes the digits 0–9 and the - symbol.

Supported characters

Character	Description
0–9	Numeric digits
-	Dash
*	Start/Stop (used internally)

How it works

Encode: Each character is converted into a sequence of bars (█) and spaces ( ) of two widths (single and double), with a space separator between symbols.

Decode:

1. Normalization: The minimum and maximum widths of each consecutive bar/space block are analysed and averaged to determine the threshold between single and double width. This allows reading barcodes scanned at any scale.
2. Block extraction: The normalized string is split into symbol blocks, separated by triple spaces.
3. Decoding: Each block is looked up in the code table to retrieve the corresponding character.

---

🔡 Code 93 Extended

What is it?

Code 93 is a high-density, high-reliability alphanumeric barcode. The Extended variant allows encoding all 128 ASCII characters using two-symbol combinations with special prefix symbols (($), (%), (/), (+)).

Supported characters

All ASCII characters from 0 to 127, including:

ASCII Range	Encoding
0–9, A–Z, -, ., , $, /, +, %	Direct symbols
a–z	Prefix (+) + uppercase letter
NUL (0)	(%)U
SOH–SUB (1–26)	($)A – ($)Z
ESC–US (27–31)	(%)A – (%)E
!, ", #, &, ', (, ), *, ,, :	Prefix (/) + letter
;, <, =, >, ?, @, [, \, ], ^, _, `, {, |, }, ~, DEL	Prefix (%) + letter

How it works

Encode:

1. The Start symbol is prepended.
2. Each character is converted to its 9-unit code (bars and spaces). Special characters use a two-symbol prefix combination.
3. Two checksums (C and K) are calculated using weighted sums modulo 47.
4. The Stop symbol and final bar (█) are appended.

Decode:

1. Normalization: Same approach as Code 11 — relative bar widths are adjusted.
2. Validation: Length, Start/Stop markers, final bar, and checksums C and K are all verified.
3. Decoding: Each 9-unit block is looked up in the table. Prefix blocks (indices 43–46) are combined with the following block to produce the final character.

Checksums

C: weighted sum of all symbols (weights 1–20 cycling right to left) modulo 47
K: weighted sum including C   (weights 1–15 cycling right to left) modulo 47

---

🧪 Tests

Category	Code 11	Code 93
Valid encode	✅	✅
Valid decode	✅	✅
Invalid decode (checksum, Start/Stop, final bar)	✅	✅
Normalization (variable-width bars)	✅	✅
Full roundtrip encode→decode	✅	✅
Roundtrip for every ASCII character (0–127)	—	✅

To run the tests:

javac -cp .:junit.jar Code11.java Code93.java Code11Test.java Code93Test.java
java  -cp .:junit.jar org.junit.runner.JUnitCore Code11Test Code93Test

---

🛠️ Technologies

• Java (no external dependencies)
• JUnit 4 for testing

---

👤 Andreu Martorell Serra

Final Java programming project — 1st year of the Higher Degree in Multiplatform Application Development (DAM).